High-frequency electrical circuits



Nov. 26, 1929. E L, P WELL 1,737,125

HIGH FREQUENCY ELECTRICAL CIRCUITS Filed June 1923 Edwb n L. Powell Patented Nov. 26, 1929 UNITED STATES PATENT caries HIGH-FREQUENCY ELECTRICAL CIRCUITS Application filed June 7, 1923.

Serial No. 643,993.

(GRANTED UNDER THE ACT OF MARCH 3, 1883, AS AMENDED APRIL 30, 1928; 370 0. G. 75'?) The principal object of my invention is to provide means for controlling current flow in high frequency electrical circuits, particularly in those circuits employing thermionic vacuum tubes having a feedback connection between the plate and grid circuits for producing oscillations or for amplifying by what is known as a regenerative action.

A further object is to improve the sharpness of resonance or selectivity of high frequency electrical circuits.

The general practice for controlling the feed-back action between the plate and grid circuits is to provide a variable coupling,

either inductive or capacitive, and through the variation of this coupling secure the desired control. This method is undesirable as such circuits are usually tuned for various purposes and when the coupling values are changed merely for the purpose of securing control over the feed-back action the tuning of the circuits is destroyed, requiring additional adjustment to return the circuits to their desired tune.

My invention will be best understood by reference to the accompanying drawing in which I have illustrated it employed in connection with radio reception. A is an antenna having inductance L and variable conso denser C permitting of tuning the circuit.

The antenna is coupled to a secondary tunable circuit containing inductance L3 and variable capacity C This circuit is contained in the grid circuit of a three electrode vacuum tube VT having its filament heated by the battery B the heating current being controlled by the rheostat R R is a resistance of the order of megohms and C is a fixed condenser forming what is known as a grid leak-stopping condenser combination. The plate circuit of the vacuum tube contains inductance L telephones T and plate battery B The condenser C provides a radio frequency bypass around the high impedance telephones.

The coupling between inductance L of the plate circuit and inductance L of grid circuit forms the required feed-back coupling between these two circuits to produce oscillations or regeneration as desired. The two coils may be Wound on the same form F and quency currents in the system. The resistance should be so constructed as ,to have a minimum of distributed capacity, as it is preferable to vary the effect of'this resistance by the use of the variable capacity in shunt therewith, and should the resistance have a large distributed capacity the desired degree of control through a shunted variable capacity will not be obtainable. By varying the capacity G4 the extent of the by-pass of radio frequency currents around the resistance It: is thoroughly under control and by a correct selection of values for these elements with a given amount of feed-back relation between the grid and plate circuits, the operator can cause the system to oscillate, or stop oscillating and regenerate to a greater or lesser degree as desired.

By a correct selection of the value for this resistance, with a given amount of feed back relation between the grid and plate circuits, the operator can cause the system to oscillate, or stop oscillating and regenerate to a greater or lesser degree as desired.

I have further found that the introduction of such a resistance in a regenerative high frequency circuit greatly improves its sharpness of resonance or selectivity. While I am unable to account for this phenomenon, the improvement is a decided one; so much so, that I have found a single circuit radio receiver of the regenerative type containing my invention equally as selective as a two or coupled circuit regenerative receiver not containing my invention.

As an example of the values which may be employed in connection with my invention, in a regenerative receiving circuit designed to operate between 200 and 600 meters wave length, I employed a very low distributed capacity resistance element of 2000 ohms having in shunt therewith a condenser variable from practically zero to .0005 microfarads.

lVhile I have illustrated and described my invention in connection with its use in a regenerative radio receiving circuit, other appli cations are readily apparent to those skilled in the art, and I do not desire to be limited to this merely illustrative use.

lVhile I have illustrated and described the oscillation controlling resistance as being effectively varied by a shunted condenser, it is readily apparent that equally efiective control may be had by providing a resistance adjustable in magnitude without necessitating other variable means connected in shunt thereto.

It has been found however, that the shunted capacity method provides a particularly smooth means of control.

The invention herein described may be manufactured and used by or for the Government of the United States for governmental purposes without the payment to me of any royalty thereon or therefor.

Having described my invention I claim In a regenerative vacuum tube detector circuit having a grid-filament and plate-filament circuits inductively coupled together, the combination in the grid-filament circuit of a coil, a variable condenser in parallel therewith, a grid-condenser and its parallel leak resistor of high ohmic resistance connected between one terminal of said condenser and the grid of said tube, means for controlling the degree of reaction between the grid-filament and plate-filament circuits comprising a second resistor of relatively low ohmic resistance connected between the other terminal of said condenser and the filament'of' said tube and a second variable condenser v in parallel with said last mentioned resistance.

EDWIN L. POWELL. 

